The present invention relates generally to electro-optic display systems and particularly to addressing such systems.
For many years the conversion of information from an electrical form into an optical form has been carried out using displays based upon vacuum tube devices such as the cathode ray tube. Such displays have proved to be very convenient and reliable in many applications. However some modern applications require displays having an adaptable shape and size which can be operated using relatively low voltages and low power and which can be manufactured relatively cheaply; as a result of these requirements much interest in the display field has been diverted from conventional displays based upon vacuum tube devices towards other kinds of display such as those based upon solid state devices and upon liquid crystals.
These other kinds of display have produced problems not previously encountered with conventional displays. One such problem is that of addressing the displays, i.e., feeding them with electrical information to convert into an optical form. Displays not using conventional vacuum tube devices consist typically of an array of display elements each of which can be addressed individually. Addressing the elements typically involves activating drive circuits with electrical control signals fed from logic circuits. The drive circuits act as electrical switches; when activated they gate electrical energising signals from an electrical source to the appropriate display element to energise those elements.
In certain cases these drive circuits cannot be made in integrated electronic circuit form because conventional integrated circuits do not have the appropriate voltage or power handling capability. As a result they have to be assembled from discrete electronic components, and their assembly is considerably time-consuming.
It is therefore an object of the invention to make the drive circuits in an integrated form so that they may be fabricated together in large numbers but in such a form that they have a reasonably high voltage or power handling capability if required.